1. Field of the Invention
This invention relates to optical scanning methods and apparatus, and more particularly, to an optical scanning method and apparatus which develops a scanned output beam from a collimated beam of light.
2. Description of the Prior Art
Optical systems for transforming a collimated beam of light into a raster scan are known in the prior art. However, many of the prior art systems are generally characterized either by considerable complexity or by limited performance. Some comparatively high performance prior art systems utilize a plurality of rotating mirrors which have a large number of facets disposed circumferentially about the axis of rotation. In order to achieve the required high scan rate and scan efficiency, comparatively large diameter polygon mirrors having a multiplicity of facets must be provided and rotated at high rates. Because of bearing strength limitations and the inability to achieve suitable dynamic balance, it has been impractical to fabricate a scanning device utilizing a single polygon mirror which is capable of being rotated at a sufficiently high R.P.M. to produce a television raster scan.
One solution to the problem experienced by prior art devices is disclosed in U.S. Pat. No. 3,782,803 (Buck). This patent discloses a flat mirror scanner including a multi-faceted pyramidal mirror which is rotated in a vertical plane, a multi-faceted polygon mirror which is rotated in a horizontal plane and a pair of spherical mirrors. The pyramidal mirror and the polygon mirror are driven by separate motors at separate rates and must be closely synchronized to generate the desired raster scan image. The pyramidal mirror rotates at a comparatively slow rate and provides vertical deflection while the polygon mirror rotates at a comparatively fast rate and provides horizontal deflection.